1. Field of Invention
The present invention relates to an interior or exterior rear mirror applicable for use in vehicles such as automobiles and particularly an electrochromic mirror that changes its reflectance with an applied voltage.
2. Description of the Related Art
Electrochromic mirrors that change their colors in a coloring reaction of a so-called “electrochromic solution”, a solution that changes its color electrically, are conventionally known (e.g., Japanese Patent No. 2672083).
Japanese Patent No. 2672083 teaches an electrochromic mirror which disposes two glass substrates in parallel with each other at a certain distance. Two transparent electrode films are respectively formed on internal surfaces of these two glass substrates which face each other. A space between the transparent electrode films is sealed with a sealant to form a cell structure. An electrochromic solution is contained in the cell. In addition, a light-reflecting film and a protective coating film are formed on a face of the glass substrate that is disposed on the opposite to the side on which light is incident.
When a voltage is applied between the respective transparent electrode films by a power supply unit in the electrochromic mirror, the reflectance of the mirror changes in a coloring reaction of the electrochromic solution.
However, in such an electrochromic mirror, if the two glass substrates are not bonded via a sealant in parallel to each other at high accuracy, images formed by the following do not coincide with each other: light which is reflected by the light-reflecting film, formed on the rear face of the glass substrate disposed on the opposite side to the side on which incident light applied; and light which is reflected by the front surface of the glass substrate which is placed on the same side as the side on which light is incident. In this case, a so-called double image is generated providing a mirror with poor visibility. Such electrochromic mirrors have the disadvantage that it is difficult and costly to manufacture them so that they do not cause the above-described phenomenon, in particular when the electrochromic mirrors are used for automobiles, which generally employ curved mirrors.
In view of overcoming these problems, an electrochromic mirror having a light-reflecting film formed on a rear face of a front glass substrate (light-entering substrate) has been proposed.
As shown in FIG. 4, the electrochromic mirror 100 has an electrochromic film 104 of tungsten trioxide (WO3) that develops color reductively formed on a rear face of the glass substrate 102 that is disposed on the same side as the side on which light is incident (the top in FIG. 4). A light-reflecting film 106, that is formed of rhodium or the like, is additionally superimposed on the electrochromic film 104. Further, an electrode film 110 is formed on a surface face (side of light-reflecting film 106) of a glass substrate 108 that is disposed on the opposite side to the incident light. An electrolyte solution 112 containing hydrogen ions is sealed in the space between the light-reflecting film 106 and the electrode film 110.
When a voltage is applied between the light-reflecting film 106 and the electrode film 110, the hydrogen ions in the electrolyte solution 112 are converted at the light-reflecting film 106 to hydrogen atoms, which diffuse through the light-reflecting film 106 to the electrochromic film 104, coloring the electrochromic film 104.
As a result, the light that enters into the glass substrate 102 and is reflected by the light-reflecting film 106 (see arrow A in FIG. 4) is reduced in intensity by passing through the colored color layer, altering the reflectance of the variable reflectance mirror. In addition, since the light that enters into the glass substrate 102 is reflected by the light-reflecting film 106 formed on the rear face of the glass substrate 102, generation of a double image is prevented.
As shown in FIG. 4, the light-reflecting film 106 is in contact with the electrolyte solution 112 in the electrochromic mirror 100 having the above configuration. Because a highly reactive liquid is generally used as the electrolyte solution 112, the light-reflecting film 106 may be corroded by the electrolyte solution 112.